This invention relates to a device for sound synthesis intended to generate a desired acoustic signal, comprising:
a first signal source intended to emit during operation a periodic signal having a given repetition frequency as a representation of the voiced parts of the desired acoustic signal, PA0 a second signal source intended to emit during operation an aperiodic signal or a noise signal as a representation of the unvoiced parts of the desired sound signal, PA0 a combination circuit intended to combine the signals of the two signal sources with each other, and PA0 a filter circuit having a variable transmission function intended to process the combined signal to derive the desired output signal.
Such a device has been described, for example, by J. Makhoul et al in the article "A mixed-source model for speech compression and synthesis", published in the Proceedings of 1978, I.E.E.E. International Conference on Acoustics, Speech and Signal Processing, Apr. 10-12, 1978, Tulsa, Okla. In this known device, besides the said signal sources, the combination circuit and the variable filter circuit, a low-pass filter is connected between the first signal source and the combination circuit and a high-pass filter is connected between the second signal source and the combination circuit.
A similar device has been described by S. H. Kwon and A. J. Goldberg in the article "An enhanced LPC vocoder with no voiced/unvoiced switch", published in I.E.E.E. Transactions on Acoustics, Speech and Signal Processing, Vol. ASSP-32, No. 4, 1984, p. 851 ff. In this known device, in addition to the said components a controlled amplifier is provided behind both the first signal source and the second signal source. Both amplifiers are controlled by a signal originating from the filter circuit having a variable transmission function in a manner such that the combination circuit can be reduced to a simple hybrid circuit.
All of these known devices have for their object to generate a speech signal having the highest possible perception quality. In practice, however, it has been found that none of the known devices reaches a speech quality which still does not require any further improvement.